Low-substituted hydroxypropyl cellulose and method for producing same

Abstract

Provided is a method for producing low-substituted hydroxypropyl cellulose having high flowability and favorable compactibility. The method includes essentially the steps of: bringing a solution of alkali metal hydroxide into contact with a powder pulp to prepare alkali cellulose; allowing the alkali cellulose and propylene oxide to react with each other to obtain a reaction product; mixing the reaction product with water, as a solubilization step, without adding any acid; neutralizing the alkali metal hydroxide contained in the reaction product; washing, dewatering and drying the neutralized reaction product after being subjected to the neutralizing step to produce dried low-substituted hydroxypropyl cellulose; and pulverizing the dried low-substituted hydroxypropyl cellulose.

What is claimed is: 
     
         1 . A method for producing low-substituted hydroxypropyl cellulose, comprising the steps of:
 bringing a solution of alkali metal hydroxide into contact with a powder pulp to prepare alkali cellulose;   allowing the alkali cellulose and propylene oxide to react with each other to obtain a reaction product;   mixing the reaction product with water, as a solubilization step, without adding any acid;   neutralizing the alkali metal hydroxide contained in the reaction product;   washing, dewatering, and drying the neutralized reaction product after being subjected to the neutralizing step to produce dried low-substituted hydroxypropyl cellulose; and   pulverizing the dried low-substituted hydroxypropyl cellulose.   
     
     
         2 . The method according to  claim 1 , wherein the ratio of the mass of water used in the solubilization step to the mass of cellulose in the powder pulp is 2.0 to 3.5. 
     
     
         3 . The method according to  claim 1 , wherein the solubilization step is performed at a mixing temperature of 30 to 40° C. 
     
     
         4 . Low-substituted hydroxypropyl cellulose that is in a form of particles, comprising:
 fine particles having a length of fiber of less than 40 μm;   spherical particles having a length of 40 μm or more and consisting of
 first spherical particles having an elongation, which is a ratio of a diameter of fiber to a length of fiber, of 0.5 or more, and 
 second spherical particles having
 an elongation of less than 0.5, 
 an aspect ratio, which is a ratio of a minimum Feret diameter to a maximum Feret diameter, of 0.5 or more, and 
 a circularity, which is a ratio of a perimeter (P EQPC ) of a circle that has the same area as a projection area of a particle to a real perimeter (P real ) of the particle, of 0.7 or more; and 
 
   fibrous particles consisting of
 long fibrous particles having a length of fiber of 200 μm or more and an elongation of less than 0.5, and consisting of
 first long fibrous particles having an aspect ratio of less than 0.5, and 
 second long fibrous particles having an aspect ratio of 0.5 or more and a circularity of less than 0.7, and 
 
 short fibrous particles having a length of fiber of 40 μm or more and less than 200 μm and an elongation of less than 0.5, and consisting of
 first short fibrous particles having an aspect ratio of less than 0.5, and 
 second short fibrous particles having an aspect ratio of 0.5 or more and a circularity of less than 0.7, 
 
   wherein the low-substituted hydroxypropyl cellulose have
 a hydroxypropoxy group content of 5 to 16% by mass, 
 a volume fraction of the spherical particles of 60 to 90% relative to all of the particles, and 
 a volume fraction ratio of the second spherical particles to the first spherical particles of 0.90 to 1.35, and 
   wherein said form of particles is classified into the fine particles, the spherical particles, and the fibrous particles on a basis of dynamic image analysis.